Fried foods are desired for their distinctive flavor and odor. To some extent in diet, they provide healthy nutrients, such as essential fatty acids, vitamins, and fiber. After cooking, the frying medium is partially absorbed by the finished (fried) food. Therefore, the quality of frying oils is important to both food consumers and to the food service industry.
The free fatty acid content of used frying oil is an indicator of frying oil deterioration and increases with time of cooking as a result of hydrolysis of triacylglycerols as well as further decomposition of hydroperoxides. The released fatty acids are more susceptible to thermal oxidation under frying temperatures than those esterfied to glycerol. The oxidized products of fatty acids impart off-flavors and off-odors (hydrolytic rancidity) to the frying medium and fried foods. Frying oil deterioration over time eventually can reach a rapidly accelerating, uncontrolled rate. K. G. Berger in an article in INFORM, 8, 812-814, 1997, suggested control of free fatty acids to about 0.4% to prevent acceleration of the break-down of frying oil fats.
The treatment and recovery of used frying oils thus is of commercial and economic importance to the food consumers and the food service industry.
Frequent filtration treatments of frying oils have been found to improve oil service life and improve health aspects of finished (cooked) food products by controlling build up of free fatty acids and removing insoluble particles. A filtration operation typically involves passing the used frying oil through a filter paper or cloth, which removes food bits and thereby reduces the chance of deleterious reactions caused by such materials in the oil. Certain adsorbents have been used to adsorb fat soluble degradation products as well as remove insoluble particles.
Commonly used adsorbents can be categorized into two subgroups; namely, natural adsorbents and synthetic adsorbents. Natural adsorbents include such materials as attapulgites, bentonites, zeolites, active carbon, kaolin, active silica, diatomaceous earth, active alumina, and active magnesia. Synthetic adsorbents have included blends of silicates with magnesium and aluminum oxides, and various silicates formed through fusing lime, magnesium, and aluminum oxides with diatomaceous earth. Dry powders of the adsorbents typically are slurried with the oil in the fryer and then circulated through a filter and returned back to the fryer until a filter bed or cake is established and the fryer is free of fines and particles. Then, the cleaned frying oil is pumped back into the fryer.
During the past ten years, various adsorbent agents have been developed. For instance, McNeil et al. in an article in J. Am. Oil Chem. Soc. 63:1564-1567, 1986, reported that a mixture of activated carbon and silica reduced 53.9% acid value and 38.3% photometric color of used frying oil, although stability of the fat may have been affected.
Mancini-Filho et al. in an article in J. Am. Oil Chem. Soc. 63:1452-1456, 1986, reported that treatment of used frying oil with a mixture of 4.5% clay, 0.5% charcoal, 2.5% magnesium oxide, and 2.5% Celite showed significant improvement in dielectric constant changes, free fatty acids, and color by 6%, 14%, and 58%, respectively. However, even though two antioxidants comprising 50 ppm butylated hydroxyanisole (BHA) and 1000 ppm ascorbyl palmitate (AP) and an antifoam agent comprising 10 ppm dimethylpolysiloxane] were added into the treated used fats, continued frying for additional 15 hours led to greater deterioration of the used oil as compared to untreated oil samples. A fresh partially hydrogenated soybean oil used at a turnover rate of 5 hours was found to increase dielectric constant changes, free fatty acids, and color after 24 hours much faster in treated oils than in untreated control oil samples.
On the other hand, daily treatment of used frying oil using Frypowder adsorbent agent maintained levels of alkaline contaminant material relatively constant over days of cooking as reported by Booth et al. in an article in Food Australia, 46:372-374, 1994. Frypowder adsorbent agent comprises porous rhyolite, citric acid and water sold commercially as a powder by MirOil Corporation, Allentown, Pa. The color darkening and foaming tendency as well as formation of polar component, conjugation, and dielectric constant of frying oil during frying also was apparently reduced by Frypowder treatment as reported by Kim et al. in an article in Korean Food Sci. Technol. 20:637-643, 19988. However, Frypowder adsorbent agent does not adsorb fatty acids due to its natural acidic characteristic, which depends on the citric acid composition, as described by Booth et al. in Food Australia, 46:372-374, 1994.
In view of the importance of the quality of frying oils to both food consumers and to the food service industry and of the commercial and economic importance of recovery of used frying oils, there continues to be a need for improved treating agents, such as adsorbent agents, useful in the treatment and recovery of used frying oils for reuse.
It is an object of the present invention to satisfy this need.